Bearings and mechanical seals have been used in various industrial applications for years. A bearing isolator is one of the components of these bearings and mechanical seals. There is a close relationship between the life of these two critical components. The failure of a mechanical seal may cause the bearings to fail and poor bearing conditions can reduce seal life. The failure of the mechanical seal results typically because of rain, product leakage, debris, and wash-down water entering the bearing housing thereby resulting in contamination of bearing lubricant, which negatively impacts lifespan of the bearings and mechanical seals.
Elastomeric lips and O-rings are used in the mechanical seals to prevent rain, product leakage, debris, and wash-down water from entering into the bearing housing of these mechanical seals thereby avoiding quick wear and tear of these elastomeric lips and the O-rings. In reality, it is very hard and almost impossible to prevent dust and exterior contaminants from entering into the interior of the bearing housing. To prevent the ingress of corruption and the egress of lubricating fluids, a number of auxiliary or improved primary sealing arrangements and devices have been provided and used in prior art sealing applications.
One such type of a seal assembly, commonly referred to as an expeller seal assembly, includes two annular, elastomeric sealing members disposed within separate annular cavities of a rotor mounted on a shaft. A stator is partially disposed between the two rotor cavities and has a central bore which defines a clearance space about the shaft. At a static sealing position, each sealing member is disposed generally against a rotor outer circumferential surface and against an adjacent radial surface on each axial end of the stator, such that the clearance space is substantially sealed at each end. When the shaft rotates, the two sealing members are pulled by frictional engagement with the rotor surface to rotate with the shaft, until centrifugal forces cause each sealing member to deflect radially outwardly from the rotor outer surface and from the stator surface. At this point, sealing in the clearance space is accomplished by a pressure differential generated by the rotation of the rotor, and the disengagement of the seal from the stator both reduces wear on the sealing members and reduces friction in the seal assembly.
However, until the rotor and sealing members reach a rotational speed sufficient to deflect the sealing members into contact with an inner circumferential surface of the rotor, such that the sealing members are again rotationally coupled with the rotor, the sealing members will lose angular momentum and deflect inwardly due to the diminished centrifugal force and return to the inner, static sealing position.
Thus, the sealing members will oscillate between the inner, static sealing position and a non-contact position until reaching a sufficient “hold-off” speed at which the sealing members remain rotationally coupled with the rotor. Also, whenever the shaft speed decreases below the hold-off speed, the sealing members will again begin to oscillate into and out of contact with the stator. As such, this oscillatory motion of the sealing members tends to increase wear and increase friction within the seal assembly.
Another type of seal is a labyrinth device which contains a tortuous path that makes it difficult for contaminants to enter the bearing housing to degrade lubricant effectiveness. The advantages of labyrinths are their non-wearing and self-venting features. Some of these commercially successful seal devices do not require any actual physical inter engagement of the sealing member parts. The disadvantages of labyrinth seal devices include higher initial costs than lip seals, and the existence of an open path to the atmosphere that can allow the contamination of the lubricant by atmospheric condensate as the housing chamber breathes during temperature fluctuations in humid environments when the equipment cycles on and off.
Therefore, an opportunity exists for improved bearing isolators having a seal member with improved life span and a unique design that will allow smaller particles or contaminants and fluids to be expelled from gaps defined between the rotor member and the stator member the same way as they entered by the expelling function of the pumping action in dynamic operations but are stopped by the sealing member when the bearing isolator is in a static condition.
Still another opportunity exists for improved bearing isolators having a seal member wherein the function and shape of the seal member can be controlled whether the rotor member and the stator member are rotatable relative one another or not.